Root/kernel/kthread.c

1/* Kernel thread helper functions.
2 * Copyright (C) 2004 IBM Corporation, Rusty Russell.
3 *
4 * Creation is done via kthreadd, so that we get a clean environment
5 * even if we're invoked from userspace (think modprobe, hotplug cpu,
6 * etc.).
7 */
8#include <linux/sched.h>
9#include <linux/kthread.h>
10#include <linux/completion.h>
11#include <linux/err.h>
12#include <linux/cpuset.h>
13#include <linux/unistd.h>
14#include <linux/file.h>
15#include <linux/export.h>
16#include <linux/mutex.h>
17#include <linux/slab.h>
18#include <linux/freezer.h>
19#include <linux/ptrace.h>
20#include <linux/uaccess.h>
21#include <trace/events/sched.h>
22
23static DEFINE_SPINLOCK(kthread_create_lock);
24static LIST_HEAD(kthread_create_list);
25struct task_struct *kthreadd_task;
26
27struct kthread_create_info
28{
29    /* Information passed to kthread() from kthreadd. */
30    int (*threadfn)(void *data);
31    void *data;
32    int node;
33
34    /* Result passed back to kthread_create() from kthreadd. */
35    struct task_struct *result;
36    struct completion *done;
37
38    struct list_head list;
39};
40
41struct kthread {
42    unsigned long flags;
43    unsigned int cpu;
44    void *data;
45    struct completion parked;
46    struct completion exited;
47};
48
49enum KTHREAD_BITS {
50    KTHREAD_IS_PER_CPU = 0,
51    KTHREAD_SHOULD_STOP,
52    KTHREAD_SHOULD_PARK,
53    KTHREAD_IS_PARKED,
54};
55
56#define __to_kthread(vfork) \
57    container_of(vfork, struct kthread, exited)
58
59static inline struct kthread *to_kthread(struct task_struct *k)
60{
61    return __to_kthread(k->vfork_done);
62}
63
64static struct kthread *to_live_kthread(struct task_struct *k)
65{
66    struct completion *vfork = ACCESS_ONCE(k->vfork_done);
67    if (likely(vfork))
68        return __to_kthread(vfork);
69    return NULL;
70}
71
72/**
73 * kthread_should_stop - should this kthread return now?
74 *
75 * When someone calls kthread_stop() on your kthread, it will be woken
76 * and this will return true. You should then return, and your return
77 * value will be passed through to kthread_stop().
78 */
79bool kthread_should_stop(void)
80{
81    return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
82}
83EXPORT_SYMBOL(kthread_should_stop);
84
85/**
86 * kthread_should_park - should this kthread park now?
87 *
88 * When someone calls kthread_park() on your kthread, it will be woken
89 * and this will return true. You should then do the necessary
90 * cleanup and call kthread_parkme()
91 *
92 * Similar to kthread_should_stop(), but this keeps the thread alive
93 * and in a park position. kthread_unpark() "restarts" the thread and
94 * calls the thread function again.
95 */
96bool kthread_should_park(void)
97{
98    return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
99}
100
101/**
102 * kthread_freezable_should_stop - should this freezable kthread return now?
103 * @was_frozen: optional out parameter, indicates whether %current was frozen
104 *
105 * kthread_should_stop() for freezable kthreads, which will enter
106 * refrigerator if necessary. This function is safe from kthread_stop() /
107 * freezer deadlock and freezable kthreads should use this function instead
108 * of calling try_to_freeze() directly.
109 */
110bool kthread_freezable_should_stop(bool *was_frozen)
111{
112    bool frozen = false;
113
114    might_sleep();
115
116    if (unlikely(freezing(current)))
117        frozen = __refrigerator(true);
118
119    if (was_frozen)
120        *was_frozen = frozen;
121
122    return kthread_should_stop();
123}
124EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
125
126/**
127 * kthread_data - return data value specified on kthread creation
128 * @task: kthread task in question
129 *
130 * Return the data value specified when kthread @task was created.
131 * The caller is responsible for ensuring the validity of @task when
132 * calling this function.
133 */
134void *kthread_data(struct task_struct *task)
135{
136    return to_kthread(task)->data;
137}
138
139/**
140 * probe_kthread_data - speculative version of kthread_data()
141 * @task: possible kthread task in question
142 *
143 * @task could be a kthread task. Return the data value specified when it
144 * was created if accessible. If @task isn't a kthread task or its data is
145 * inaccessible for any reason, %NULL is returned. This function requires
146 * that @task itself is safe to dereference.
147 */
148void *probe_kthread_data(struct task_struct *task)
149{
150    struct kthread *kthread = to_kthread(task);
151    void *data = NULL;
152
153    probe_kernel_read(&data, &kthread->data, sizeof(data));
154    return data;
155}
156
157static void __kthread_parkme(struct kthread *self)
158{
159    __set_current_state(TASK_PARKED);
160    while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
161        if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
162            complete(&self->parked);
163        schedule();
164        __set_current_state(TASK_PARKED);
165    }
166    clear_bit(KTHREAD_IS_PARKED, &self->flags);
167    __set_current_state(TASK_RUNNING);
168}
169
170void kthread_parkme(void)
171{
172    __kthread_parkme(to_kthread(current));
173}
174
175static int kthread(void *_create)
176{
177    /* Copy data: it's on kthread's stack */
178    struct kthread_create_info *create = _create;
179    int (*threadfn)(void *data) = create->threadfn;
180    void *data = create->data;
181    struct completion *done;
182    struct kthread self;
183    int ret;
184
185    self.flags = 0;
186    self.data = data;
187    init_completion(&self.exited);
188    init_completion(&self.parked);
189    current->vfork_done = &self.exited;
190
191    /* If user was SIGKILLed, I release the structure. */
192    done = xchg(&create->done, NULL);
193    if (!done) {
194        kfree(create);
195        do_exit(-EINTR);
196    }
197    /* OK, tell user we're spawned, wait for stop or wakeup */
198    __set_current_state(TASK_UNINTERRUPTIBLE);
199    create->result = current;
200    complete(done);
201    schedule();
202
203    ret = -EINTR;
204
205    if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
206        __kthread_parkme(&self);
207        ret = threadfn(data);
208    }
209    /* we can't just return, we must preserve "self" on stack */
210    do_exit(ret);
211}
212
213/* called from do_fork() to get node information for about to be created task */
214int tsk_fork_get_node(struct task_struct *tsk)
215{
216#ifdef CONFIG_NUMA
217    if (tsk == kthreadd_task)
218        return tsk->pref_node_fork;
219#endif
220    return NUMA_NO_NODE;
221}
222
223static void create_kthread(struct kthread_create_info *create)
224{
225    int pid;
226
227#ifdef CONFIG_NUMA
228    current->pref_node_fork = create->node;
229#endif
230    /* We want our own signal handler (we take no signals by default). */
231    pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
232    if (pid < 0) {
233        /* If user was SIGKILLed, I release the structure. */
234        struct completion *done = xchg(&create->done, NULL);
235
236        if (!done) {
237            kfree(create);
238            return;
239        }
240        create->result = ERR_PTR(pid);
241        complete(done);
242    }
243}
244
245/**
246 * kthread_create_on_node - create a kthread.
247 * @threadfn: the function to run until signal_pending(current).
248 * @data: data ptr for @threadfn.
249 * @node: memory node number.
250 * @namefmt: printf-style name for the thread.
251 *
252 * Description: This helper function creates and names a kernel
253 * thread. The thread will be stopped: use wake_up_process() to start
254 * it. See also kthread_run().
255 *
256 * If thread is going to be bound on a particular cpu, give its node
257 * in @node, to get NUMA affinity for kthread stack, or else give -1.
258 * When woken, the thread will run @threadfn() with @data as its
259 * argument. @threadfn() can either call do_exit() directly if it is a
260 * standalone thread for which no one will call kthread_stop(), or
261 * return when 'kthread_should_stop()' is true (which means
262 * kthread_stop() has been called). The return value should be zero
263 * or a negative error number; it will be passed to kthread_stop().
264 *
265 * Returns a task_struct or ERR_PTR(-ENOMEM).
266 */
267struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
268                       void *data, int node,
269                       const char namefmt[],
270                       ...)
271{
272    DECLARE_COMPLETION_ONSTACK(done);
273    struct task_struct *task;
274    struct kthread_create_info *create = kmalloc(sizeof(*create),
275                             GFP_KERNEL);
276
277    if (!create)
278        return ERR_PTR(-ENOMEM);
279    create->threadfn = threadfn;
280    create->data = data;
281    create->node = node;
282    create->done = &done;
283
284    spin_lock(&kthread_create_lock);
285    list_add_tail(&create->list, &kthread_create_list);
286    spin_unlock(&kthread_create_lock);
287
288    wake_up_process(kthreadd_task);
289    /*
290     * Wait for completion in killable state, for I might be chosen by
291     * the OOM killer while kthreadd is trying to allocate memory for
292     * new kernel thread.
293     */
294    if (unlikely(wait_for_completion_killable(&done))) {
295        /*
296         * If I was SIGKILLed before kthreadd (or new kernel thread)
297         * calls complete(), leave the cleanup of this structure to
298         * that thread.
299         */
300        if (xchg(&create->done, NULL))
301            return ERR_PTR(-ENOMEM);
302        /*
303         * kthreadd (or new kernel thread) will call complete()
304         * shortly.
305         */
306        wait_for_completion(&done);
307    }
308    task = create->result;
309    if (!IS_ERR(task)) {
310        static const struct sched_param param = { .sched_priority = 0 };
311        va_list args;
312
313        va_start(args, namefmt);
314        vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
315        va_end(args);
316        /*
317         * root may have changed our (kthreadd's) priority or CPU mask.
318         * The kernel thread should not inherit these properties.
319         */
320        sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
321        set_cpus_allowed_ptr(task, cpu_all_mask);
322    }
323    kfree(create);
324    return task;
325}
326EXPORT_SYMBOL(kthread_create_on_node);
327
328static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
329{
330    /* Must have done schedule() in kthread() before we set_task_cpu */
331    if (!wait_task_inactive(p, state)) {
332        WARN_ON(1);
333        return;
334    }
335    /* It's safe because the task is inactive. */
336    do_set_cpus_allowed(p, cpumask_of(cpu));
337    p->flags |= PF_NO_SETAFFINITY;
338}
339
340/**
341 * kthread_bind - bind a just-created kthread to a cpu.
342 * @p: thread created by kthread_create().
343 * @cpu: cpu (might not be online, must be possible) for @k to run on.
344 *
345 * Description: This function is equivalent to set_cpus_allowed(),
346 * except that @cpu doesn't need to be online, and the thread must be
347 * stopped (i.e., just returned from kthread_create()).
348 */
349void kthread_bind(struct task_struct *p, unsigned int cpu)
350{
351    __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
352}
353EXPORT_SYMBOL(kthread_bind);
354
355/**
356 * kthread_create_on_cpu - Create a cpu bound kthread
357 * @threadfn: the function to run until signal_pending(current).
358 * @data: data ptr for @threadfn.
359 * @cpu: The cpu on which the thread should be bound,
360 * @namefmt: printf-style name for the thread. Format is restricted
361 * to "name.*%u". Code fills in cpu number.
362 *
363 * Description: This helper function creates and names a kernel thread
364 * The thread will be woken and put into park mode.
365 */
366struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
367                      void *data, unsigned int cpu,
368                      const char *namefmt)
369{
370    struct task_struct *p;
371
372    p = kthread_create_on_node(threadfn, data, cpu_to_mem(cpu), namefmt,
373                   cpu);
374    if (IS_ERR(p))
375        return p;
376    set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
377    to_kthread(p)->cpu = cpu;
378    /* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
379    kthread_park(p);
380    return p;
381}
382
383static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
384{
385    clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
386    /*
387     * We clear the IS_PARKED bit here as we don't wait
388     * until the task has left the park code. So if we'd
389     * park before that happens we'd see the IS_PARKED bit
390     * which might be about to be cleared.
391     */
392    if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
393        if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
394            __kthread_bind(k, kthread->cpu, TASK_PARKED);
395        wake_up_state(k, TASK_PARKED);
396    }
397}
398
399/**
400 * kthread_unpark - unpark a thread created by kthread_create().
401 * @k: thread created by kthread_create().
402 *
403 * Sets kthread_should_park() for @k to return false, wakes it, and
404 * waits for it to return. If the thread is marked percpu then its
405 * bound to the cpu again.
406 */
407void kthread_unpark(struct task_struct *k)
408{
409    struct kthread *kthread = to_live_kthread(k);
410
411    if (kthread)
412        __kthread_unpark(k, kthread);
413}
414
415/**
416 * kthread_park - park a thread created by kthread_create().
417 * @k: thread created by kthread_create().
418 *
419 * Sets kthread_should_park() for @k to return true, wakes it, and
420 * waits for it to return. This can also be called after kthread_create()
421 * instead of calling wake_up_process(): the thread will park without
422 * calling threadfn().
423 *
424 * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
425 * If called by the kthread itself just the park bit is set.
426 */
427int kthread_park(struct task_struct *k)
428{
429    struct kthread *kthread = to_live_kthread(k);
430    int ret = -ENOSYS;
431
432    if (kthread) {
433        if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
434            set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
435            if (k != current) {
436                wake_up_process(k);
437                wait_for_completion(&kthread->parked);
438            }
439        }
440        ret = 0;
441    }
442    return ret;
443}
444
445/**
446 * kthread_stop - stop a thread created by kthread_create().
447 * @k: thread created by kthread_create().
448 *
449 * Sets kthread_should_stop() for @k to return true, wakes it, and
450 * waits for it to exit. This can also be called after kthread_create()
451 * instead of calling wake_up_process(): the thread will exit without
452 * calling threadfn().
453 *
454 * If threadfn() may call do_exit() itself, the caller must ensure
455 * task_struct can't go away.
456 *
457 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
458 * was never called.
459 */
460int kthread_stop(struct task_struct *k)
461{
462    struct kthread *kthread;
463    int ret;
464
465    trace_sched_kthread_stop(k);
466
467    get_task_struct(k);
468    kthread = to_live_kthread(k);
469    if (kthread) {
470        set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
471        __kthread_unpark(k, kthread);
472        wake_up_process(k);
473        wait_for_completion(&kthread->exited);
474    }
475    ret = k->exit_code;
476    put_task_struct(k);
477
478    trace_sched_kthread_stop_ret(ret);
479    return ret;
480}
481EXPORT_SYMBOL(kthread_stop);
482
483int kthreadd(void *unused)
484{
485    struct task_struct *tsk = current;
486
487    /* Setup a clean context for our children to inherit. */
488    set_task_comm(tsk, "kthreadd");
489    ignore_signals(tsk);
490    set_cpus_allowed_ptr(tsk, cpu_all_mask);
491    set_mems_allowed(node_states[N_MEMORY]);
492
493    current->flags |= PF_NOFREEZE;
494
495    for (;;) {
496        set_current_state(TASK_INTERRUPTIBLE);
497        if (list_empty(&kthread_create_list))
498            schedule();
499        __set_current_state(TASK_RUNNING);
500
501        spin_lock(&kthread_create_lock);
502        while (!list_empty(&kthread_create_list)) {
503            struct kthread_create_info *create;
504
505            create = list_entry(kthread_create_list.next,
506                        struct kthread_create_info, list);
507            list_del_init(&create->list);
508            spin_unlock(&kthread_create_lock);
509
510            create_kthread(create);
511
512            spin_lock(&kthread_create_lock);
513        }
514        spin_unlock(&kthread_create_lock);
515    }
516
517    return 0;
518}
519
520void __init_kthread_worker(struct kthread_worker *worker,
521                const char *name,
522                struct lock_class_key *key)
523{
524    spin_lock_init(&worker->lock);
525    lockdep_set_class_and_name(&worker->lock, key, name);
526    INIT_LIST_HEAD(&worker->work_list);
527    worker->task = NULL;
528}
529EXPORT_SYMBOL_GPL(__init_kthread_worker);
530
531/**
532 * kthread_worker_fn - kthread function to process kthread_worker
533 * @worker_ptr: pointer to initialized kthread_worker
534 *
535 * This function can be used as @threadfn to kthread_create() or
536 * kthread_run() with @worker_ptr argument pointing to an initialized
537 * kthread_worker. The started kthread will process work_list until
538 * the it is stopped with kthread_stop(). A kthread can also call
539 * this function directly after extra initialization.
540 *
541 * Different kthreads can be used for the same kthread_worker as long
542 * as there's only one kthread attached to it at any given time. A
543 * kthread_worker without an attached kthread simply collects queued
544 * kthread_works.
545 */
546int kthread_worker_fn(void *worker_ptr)
547{
548    struct kthread_worker *worker = worker_ptr;
549    struct kthread_work *work;
550
551    WARN_ON(worker->task);
552    worker->task = current;
553repeat:
554    set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
555
556    if (kthread_should_stop()) {
557        __set_current_state(TASK_RUNNING);
558        spin_lock_irq(&worker->lock);
559        worker->task = NULL;
560        spin_unlock_irq(&worker->lock);
561        return 0;
562    }
563
564    work = NULL;
565    spin_lock_irq(&worker->lock);
566    if (!list_empty(&worker->work_list)) {
567        work = list_first_entry(&worker->work_list,
568                    struct kthread_work, node);
569        list_del_init(&work->node);
570    }
571    worker->current_work = work;
572    spin_unlock_irq(&worker->lock);
573
574    if (work) {
575        __set_current_state(TASK_RUNNING);
576        work->func(work);
577    } else if (!freezing(current))
578        schedule();
579
580    try_to_freeze();
581    goto repeat;
582}
583EXPORT_SYMBOL_GPL(kthread_worker_fn);
584
585/* insert @work before @pos in @worker */
586static void insert_kthread_work(struct kthread_worker *worker,
587                   struct kthread_work *work,
588                   struct list_head *pos)
589{
590    lockdep_assert_held(&worker->lock);
591
592    list_add_tail(&work->node, pos);
593    work->worker = worker;
594    if (likely(worker->task))
595        wake_up_process(worker->task);
596}
597
598/**
599 * queue_kthread_work - queue a kthread_work
600 * @worker: target kthread_worker
601 * @work: kthread_work to queue
602 *
603 * Queue @work to work processor @task for async execution. @task
604 * must have been created with kthread_worker_create(). Returns %true
605 * if @work was successfully queued, %false if it was already pending.
606 */
607bool queue_kthread_work(struct kthread_worker *worker,
608            struct kthread_work *work)
609{
610    bool ret = false;
611    unsigned long flags;
612
613    spin_lock_irqsave(&worker->lock, flags);
614    if (list_empty(&work->node)) {
615        insert_kthread_work(worker, work, &worker->work_list);
616        ret = true;
617    }
618    spin_unlock_irqrestore(&worker->lock, flags);
619    return ret;
620}
621EXPORT_SYMBOL_GPL(queue_kthread_work);
622
623struct kthread_flush_work {
624    struct kthread_work work;
625    struct completion done;
626};
627
628static void kthread_flush_work_fn(struct kthread_work *work)
629{
630    struct kthread_flush_work *fwork =
631        container_of(work, struct kthread_flush_work, work);
632    complete(&fwork->done);
633}
634
635/**
636 * flush_kthread_work - flush a kthread_work
637 * @work: work to flush
638 *
639 * If @work is queued or executing, wait for it to finish execution.
640 */
641void flush_kthread_work(struct kthread_work *work)
642{
643    struct kthread_flush_work fwork = {
644        KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
645        COMPLETION_INITIALIZER_ONSTACK(fwork.done),
646    };
647    struct kthread_worker *worker;
648    bool noop = false;
649
650retry:
651    worker = work->worker;
652    if (!worker)
653        return;
654
655    spin_lock_irq(&worker->lock);
656    if (work->worker != worker) {
657        spin_unlock_irq(&worker->lock);
658        goto retry;
659    }
660
661    if (!list_empty(&work->node))
662        insert_kthread_work(worker, &fwork.work, work->node.next);
663    else if (worker->current_work == work)
664        insert_kthread_work(worker, &fwork.work, worker->work_list.next);
665    else
666        noop = true;
667
668    spin_unlock_irq(&worker->lock);
669
670    if (!noop)
671        wait_for_completion(&fwork.done);
672}
673EXPORT_SYMBOL_GPL(flush_kthread_work);
674
675/**
676 * flush_kthread_worker - flush all current works on a kthread_worker
677 * @worker: worker to flush
678 *
679 * Wait until all currently executing or pending works on @worker are
680 * finished.
681 */
682void flush_kthread_worker(struct kthread_worker *worker)
683{
684    struct kthread_flush_work fwork = {
685        KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
686        COMPLETION_INITIALIZER_ONSTACK(fwork.done),
687    };
688
689    queue_kthread_work(worker, &fwork.work);
690    wait_for_completion(&fwork.done);
691}
692EXPORT_SYMBOL_GPL(flush_kthread_worker);
693

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